1ESAC_3_24_05.ppt

GLAST: GLAST: Large Area TelescopeLarge Area Telescope

- LAT Status and Schedule

- Multiwavelength Needs: Discussion with AAAC in October

Peter F. Michelson Stanford University peterm@stanford.edu

GLAST User’s Committee GLAST User’s Committee November 8, 2005November 8, 2005

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LAT development status

e+ e–

Calorimeter

Tracker

ACD

LAT: 20 MeV – >300 GeV

GBM: 10 keV – 25 MeV

► 16 towers integrated;

► ACD integration - November 15, 2005

► LAT shipment from SLAC to NRL for environmental testing - January 24, 2006

► LAT shipment to General Dynamics for observatory integration - June 2006

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LAT Silicon Trackerteam effort involving ~70 physicists and engineers from Italy (INFN & ASI), the United States, and Japan

LAT TKR performance

98

98.5

99

99.5

100

A B 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Eff

icie

ncy

(%

)

0

0.5

1

1.5

2

Ba

d c

han

nels

(%

)

Efficiency Bad chans fraction

specspec

specspec

11,500 sensors350 trays18 towers

~106 channels83 m2 Si surface

INFN, Pisa

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LAT Calorimeterteam effort involving physicists and engineers from the United States, France (IN2P3 & CEA), and Sweden

NRL

1,728 CsI crystal detector elements

18 modules

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LAT Anti-Coincidence Detectorteam effort involving physicists and engineers from Goddard Space Flight Center, SLAC, and Fermi Lab

ACD before installation of Micrometeoroid Shield

ACD with Micrometeoroid Shield and Multi-Layer Insulation (but without Germanium Kapton outer layer)

NASA-GSFC

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LAT integration and test status

► LAT proceeding towards June 2006 RFI to observatory

► LAT collaborators in France, Italy, Japan, and Sweden have been key contributors

I&T facility at Stanford University / SLAC

-ray event in 1st integrated tower

LAT is possible because of partnership between

– particle physicists & astrophysicists,

– SLAC & GSFC,– DOE & NASA

NASADOE

LIPL

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16-tower movie

rate: ~500 Hz

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8-tower movie – photon events

rate: ~1Hz

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Discussion with AAAC

presentation to AAAC in October 2005

– GLAST status report

– summary of multiwavelength needs and need for recognizing agency interdependencies

– informed AAAC that LAT Collaboration is developing a multiwavelength implementation plan to address critical needs

GLAST also highlighted in presentations by Anne Kinney (NASA) and Robin Staffin (DOE)

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GLAST: Multiwavelength needs Some key science objectives:

– understand particle acceleration and high-energy emission in neutron stars and black holes

– determine origin(s) of -ray extragalactic diffuse background

– measure extragalactic background starlight

– search for dark matter

“.. GLAST will focus on the most energetic objects and phenomena in the universe…”

multiwavelength observations important to several science objectives

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Multiwavelength observations are important for GLAST

► Multiwavelength observations needed for

• understanding the high-energy diffuse emission of the Milky Way

• source identification and population studies

• intensive exploration of the brightest and most variable sources that will allow deep study of the source physics

• rapid follow-up on transients (e.g. GRBs, blazar flares)• GLAST mission designed to support rapid notification for follow-up

example: Markarian 421

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Science opportunities

Many opportunities for exciting discoveries:– origin(s) of the high-energy extragalactic diffuse background

– extragalactic background starlight to z > 3

– new physics & the unknown! (e.g. dark matter, extra dimensions, big bang relics)

– -ray emission from clusters of galaxies; cosmic-ray acceleration and confinement on large scales

– -rays from Ultra-Luminous Infrared Galaxies; cosmic ray acceleration efficiency and star formation rate

– high-latitude Galactic Inverse-Compton emission and thereby measure TeV-scale CR electrons in the Galaxy

– high-energy emission from Galactic pulsars and their birth places

-ray sky (>100 MeV) 85% galactic diffuse emission

~5% isotropic emission

10% point sources

EGRET GLAST

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-ray Sources: Multiwavelength observations are important

• Nature rarely produces mono-energetic particle beams. Broad range of particle energies leads to broad range of photon energies.

– example: o production

• Charged particles rarely interact by only one process. Different processes radiate in different energy bands.

– example: synchrotron-Compton processes

• High-energy particles needed to produce gamma rays can radiate in lower-energy bands as they lose energy.

– example: gamma-ray burst afterglows

Sources are non-thermal: produced by interactions of energetic particles

GLAST LAT

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Science opportunities & multiwavelength needs

3rd EGRET Catalog(271 sources)GLAST all-sky survey (~104 sources)

EGRET (>100 MeV) 85% galactic diffuse emission

~5% isotropic emission

10% point sources

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-ray source localization

multi-wavelength approach to -ray source identification:

- localization- variability

source localization (68% radius)- -ray bursts: 1 to tens arcminutes- unid EGRET sources: 0.3’ – 1’

Unidentified EGRET sources

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Diffuse -ray emission from the Milky Way

Halo

Gas, sources

Sun

Intergalactic space

► This foreground needs to be well characterized for analysis of LAT data, much more so than for EGRET, owing to vastly better statistics and better angular resolution

► The origin is cosmic-ray interactions with interstellar gas and the interstellar radiation field

► Fundamental questions remain from EGRET with results limited by knowledge of the diffuse emission; e.g.

– particle dark matter;

– the isotropic -ray background

85% of the celestial gamma-ray emission

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particle dark matter

► The lightest supersymmetric particle is a plausible dark matter candidate, most likely with mass > ~50 GeV

► Annihilation channels produce -ray lines and continuum, and secondary electrons that in turn can produce -rays

► WIMPs would be distributed in a Galactic halo, with a central density enhancement of uncertain cuspiness,

– most likely the halo will have significant substructure, which is important as the annihilation rate ~2

inclusive flux, or or Z“lines”?

q

q

► we need to improve the precision of the galactic diffuse emission model

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Modeling diffuse emission: need for new data► Extend CO surveys to high latitudes

– newly-found small molecular clouds will otherwise be interpreted as unidentified sources, and clearly limit dark matter studies

► C18O observations (optically thin tracer) of special directions (e.g. Galactic center, arm tangents)

– assess whether velocity crowding is affecting calculations of molecular column density, and for carefully pinning down the diffuse emission

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0

-20

-40

Gal

acti

c L

atit

ud

e

220 200 180 160 140 120 100 80 60 40 20 0

CfA 1.2mGalactic Longitude

Dam

e, H

artman

n, & T

haddeus (200

1)D

ame

& T

haddeus (20

04)

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Extragalactic -ray background► origin is a mystery; either sources there for GLAST to

resolve (and study!) OR there is a truly diffuse flux from the early Universe

EGRET constrains blazars to be > 25% of diffuse;

annihilation of cosmological neutralinos has, in principle, a distinctive spectral signature

from Elsässer & Mannheim, Phys. Rev. Lett. (2005)

LAT baseline background limit

Energy (keV)

E2 d

J/dE

(keV

/(cm

2-s

-keV

-sr)

EGRET

steep-spectrum quasars

Seyfert II galaxies

Seyfert I galaxies

Type 1a Supernovae

discovery spacediscovery space• blazars• normal galaxies• cluster mergers• primordial diffuse• new physics

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Physics in the Extreme Environments of Pulsars

• sites of interactions in extreme gravitational, electric, and magnetic fields.

• key to deciphering these extreme conditions is having accurate, absolute timing data for many pulsars.

• with the exception of a few X-ray pulsars, radio band provides the needed timing information. A sizeable radio timing program is beyond the scope of routine radio pulsar programs.

Multiwavelength light curves of gamma-ray pulsars- their diversity shows the need for a larger sample with better detail, including phase-resolved spectra at all wavelengths.

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Probing Extragalactic Background StarLight with Blazars

No significant attenuation below 10 GeV

-ray energy (GeV)

op

acit

y

fo

r so

urc

e at

z

opaque

► diffuse EBL contains unique information about the epochs of formation and the evolution of galaxies

► direct EBL measurements require accurate model-based subtraction of bright foregrounds (e.g., zodiacal light)

► alternative approach: extract imprint of EBL absorption, as function of redshift, from high-energy spectra of extragalactic sources

e+e- , maximum when

EBL ~ ½ (1000 GeV / E) eV

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TeV (HESS) blazar constraints on EBL

- lower limits on HST galaxy counts combined with HESS upper limit on EBL imply that any unresolved component is no more than ~1/3 of the total.

EBL spectral energy distribution

integrated light from galaxy counts

reference EBL SED, matches direct measurements at 2.2 and 3.5 m.

HESS upper limit derived from observed hard spectra of blazars at z = 0.165 and 0.186

GLAST

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70% of EGRET sources (|b|>10o) are blazars

4.8 GHz radio survey; chose bright flat-spectrum sources

95% of radio-selected sources are blazars

Probing Extragalactic Background StarLight with Blazars

model A

model B

measure flux E>10 GeV/flux E>1 GeVGLAST science objective:

measure the redshift dependence of the attenuation of flux above 10 GeV for a sample of high-redshift blazars

sensitive to optical-UV EBLsensitive to optical-UV EBL

radio-selected blazar survey

(~60% complete)

EGRET blazars

26 objects Z > 3

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Summary of Critical Multiwavelength Needs

Science Objective GLAST provides multi-requirementsDifferential measurement (vs Z) of extragalactic background light to Z ~5.5

Measurement of blazar spectra in band where cutoffs are expected from + ebl → e+ + e-

Broadband contemporaneous / simultaneous spectral measurements (radio, optical, X-ray, TeV) of blazar spectra, particularly around the synchrotron peak;

Resolve origin of particle acceleration and emission mechanisms in systems with relativistic jets, supermassive black holes

All-sky monitoring coverage of blazar flares and GRBs

radio and optical surveys of flat-spectrum radio sources to extend blazar catalogs

Reliable model of Milky Way diffuse emission required for accurate source localization and to facilitate search for dark matter

Mapping of cosmic ray interactions with all forms of interstellar matter.

Extend CO surveys to high galactic latitude;

survey special directions (eg. spiral arms, galactic center) with optically thin tracer (C18O)

Understand particle acceleration and emission mechanisms in extreme environment (gravity, electric and magnetic fields) of rotating neutron stars

Spectra and light curves resulting from primary interactions of the most energetic particles.

Contemporaneous radio and X-ray pulsar timing observations

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Importance of national facilities► GLAST operations depend on NASA and DOE facilities:

– NASA / GSFC: mission operations, science support center / MSFC: GBM instrument operations

– DOE / SLAC: LAT instrument operations; level-1 data processing pipeline

► science is connected across facilities and agencies

- GLAST is scientifically connected to, for example,

- NRAO (VLA, VLBA, Greenbank) - NSF

- NOAO - NSF

- VERITAS - NSF/DOE

► actions by one agency on one project can affect science; important for agencies to recognize interdependencies

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Summary

► Integration & test of all GLAST components underway.– LAT expected to be ready for observatory integration: June 2006– GLAST launch: August 31, 2007– DOE–NASA partnership on the Large Area Telescope is a

success !!

► GLAST will provide a major new capability for addressing important science questions.

– optimal use will require extensive coordinated and, in some cases, simultaneous observations from radio to TeV energies

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Backup slides

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DM signal from Galactic center ?

– all of these depend on the model for diffuse emission

► Recent re-analyses of EGRET data suggest

– source not coincident with the Galactic center itself

– variable, too, although systematics are significant (Nolan et al. 2003)

► Many complications affect modeling the diffuse emission of this region & therefore the current results

► Spectrum, position, variability, and potentially angular extent provide clues about nature of the EGRET G.C. source

Hooper & Dingus (2002)

Yusef-Zadeh (2002)

20 cm radio continuum

Sgr A*

CS (2-1) lineCS (2-1) line

3EG J1746-2851 confidence region

Sgr A East

>5 GeV -rays

Arches cluster (~150 O stars)

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Modeling diffuse emission of the Milky Way

► Nature has given us some breaks

– Radiative transfer is simple – once -rays are produced, they propagate without scattering or absorption

– CRs tend to be much more smoothly distributed than the interstellar gas

– Good tracers of the gas exist for most regions, with Doppler shift measurements obviating to a large extent the disadvantage of our in-plane perspective

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Diffuse -ray emission from the Milky Way

EGRET (>100 MeV)

► Milky Way: bright celestial background in high-energy -rays (approx. 85% of EGRET -rays)

► GLAST LAT science goals require a model for the Milky Way background that is reliable:

– on large scales (absolute intensities of extended sources),

– on small scales (positions and fluxes of sources)

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Growing Science Community Involvement

► At all mission levels: Science Working Group, User’s Committee, Conferences, Workshops.

► Multiwavelength survey initiatives underway

─ VLA monitoring for a large sample of flat-spectrum, compact sources (Ulvestad, et al.)

─ VLBA Imaging and Polarimetry Survey proposed to obtain a set of reference images for 1000 potential LAT sources in advance of GLAST launch (Taylor, Ulvestad, Readhead, Blandford, et al.).

─ Northern and Southern hemisphere radio pulsar timing campaigns in support of GLAST mission (Thorsett, et al. ; Manchester, et al.)

─ optical monitoring of LAT AGN

► Broad and growing interest

COS-B 1975-1982 11 481

EGRET 1991-2000 53 1212

GLAST 2007- 404 ???

Publications & Conference Proceedings

pre-launch total

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GLAST: Exploring the High-Energy Universe

gamma rays provide a direct view into Nature’s largest accelerators

the Universe is mainly transparent to rays: can probe cosmological volumes. Any opacity is energy-dependent.

huge leap in key capabilities, including a largely unexplored energy range; great potential for Discovery

– recognized by the National Academy of Sciences 2000 Decadal Survey (Taylor-McKee): GLAST is top-ranked mission in its category

also featured in NAS Connecting Quarks with the Cosmos and the Physics of the Universe 2004 Strategic plan:

“…GLAST will focus on the most energetic objects and phenomena in the

universe…it will also search for Dark Matter candidate particles.”